The problem is on line 86 of ProcessReg you are trying to call a method on an object, but the reference you have to that object == null, hence the NullPointerException.

Find that reference, and decide whether it being null at that point in the control flow is an error or not. If it's an error, fix that. If it's not an error, wait until you've set it to point to an object before using it to call methods on that object.

UPDATE

Now you've posted your code for DBConnection, it's clear there are many issues with your code. I'll try to point out the main ones, but as an aside I'd seriously recommend brushing up on the Java fundamentals here before going on to write relatively complex pieces of functionality like Servlets etc.

Issues in ProcessReg

you are calling getConnection() and returning con, but you haven't initialised con yet so you're just returning a null reference.

you are then trying to cast the Connection reference returned from getConnection() to the Statement type. This will throw a ClassCastException. Instead you'll want to call createStatement() on the returned Connection object reference.

all the methods on DbConnect are static (see below - you should refactor this) so you're instantiating a pointless DBConnect object a, then obviously never using it.

Issues in DBConnect

you have a static field con, and static methods to modify/access it. Don't do this. Make con an instance variable and tuck the initialisation inside the DBConnect constructor - something like this:

Problem is public static Connection getConnection() method returns a null connection as you are never calling createConnection() whhich actually loads the driver and creates the connection object. You need to fix your getConnection() to call createConnection() before returning con object in DBConnect class.

Why did you set return value of getConnection() method to variable of Statement type?

stmt = (Statement) DBConnect.getConnection();

For what purpose do you cast it to Statement? It would be need only if your method returns the Object refernce type. Casting is not necessary if the return type is subinterface or any implementation of Statement. And casting of Connection to Statement cannot be executed.